1. Field of the Invention
The present invention relates to a power source monitor that monitors the state of charge of a power source apparatus mounted in a vehicle.
2. Description of the Related Art
In recent years, there has been developed a vehicle in which as a technology for reducing fuel consumption by the vehicle, kinetic energy is recovered, as electric power, through regenerative power generation when the vehicle is decelerated. There has been developed a vehicle in which for the purpose of efficiently performing regenerative power generation, a battery (e.g., a lithium-ion battery) having a large charging/discharging allowable capacity and a high energy density is mounted. In the case of such a battery as described above, for the purpose of lengthen the lifetime and raising the safety of the battery, the state of charge (referred to as SOC, hereinafter) of the battery need to be monitored more strictly than in the case of a lead battery so that the battery is prevented from being overcharged or overdischarged. In addition, in order to increase the amount of recovery, it is important to comprehend and manage the SOC of the battery.
In a vehicle utilizing a conventional lead battery, when the lead battery discharges, deterioration develops; therefore, the SOC is always controlled so as to keep the lead battery almost fully charged. The SOC of the lead battery is estimated in the following manner. After the vehicle has been started, the amount of charge in the lead battery is increased, and when the amount of charge in the lead battery is saturated and hence the current value becomes small, it is considered that the lead battery has been fully charged; then, from the timing of the full charging, the amount of charging and discharging currents are integrated for the purpose of estimating the SOC of the battery. For example, with regard to a vehicle equipped with a lead battery and a power-generation motor that can operate as both an electric power generator and a motor, there has been proposed a battery state monitoring apparatus (e.g., refer to Patent Document 1). In the battery state monitoring apparatus, after the internal combustion engine of the vehicle has been started, power generation by the power-generation motor is once interrupted so as to make the battery discharge; the charging current for the battery is gradually increased under the condition that the polarization states inside the battery have been made uniform; when the charging current for the battery becomes minute, the SOC is estimated from the voltage across the battery.